This proposal is to complete an ongoing mapping of genes involved in axis defects in mice and move on to study a new and cloned zebrafish neurogenic mutation. One ultimate goal is to make a model of it in mouse. To date, a number of model organisms have been used in the study of molecular development: those that have really good genetics or ones for which developing stages are readily accessible but for technical reasons genetic studies are not an option. Recently, zebrafish have come into use because it satisfies both criteria. Among its advantages are that it is a vertebrate, hundreds of embryos can be obtained in a day, the embryos are transparent and can be easily visualized. Thus, novel phenotypes in early neural development are evident whereas they would be inaccessible in a mammal. In a retroviral mutant screen in zebrafish, a mutation has a viral tag that can be used to easily clone it. From the Hopkins screen at MIT, I have chosen to analyze a recessive lethal (Hi904) that causes disorganization and tumor-like overgrowth of the nervous system. The gene has been cloned and is novel. We will do experiments that are easily accomplished in fish, and the rest in mice where we can recreate the mutation by homologous recombination. The experiments in zebrafish will include: expression studies of Hi904 message in embryos, analysis with well-characterized molecular markers to assess cell number in the nervous system of mutant embryos, and also patterning and state of differentiation. This will be accomplished by in situ hybridization and antibody staining. The experiments in mice will include: obtaining the complete mouse cDNAs including expected alternative splice forms, expression analysis in normal and tumor tissues and in situ hybridization in embryos. We will address tumorigenicity by transplanting mutant fish cells into nude mice. We will make antibody for functional studies. Mutations in mouse will be generated using homologous recombination. The biochemical and cellular function of Hi904 protein will be explored by studying its localization and interactions. It is expected that this set of genes will define a new tumor suppressor that plays-a role in the development of primitive neuroectodermal tumors of children.